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Alan Turing's "Delilah" project

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I suppose some of this is a "lost story" but I wrote about Delilah back in 2012: https://blog.jgc.org/2012/03/delilah-secure-speech-system.ht... and the actual system is on display at Bletchley.

The incoming signal is turned into 4000 bits per second then XORed with a large pseudorandom sequence.[1]. It's quite interesting what was possible given such limited hardware at the time.

I've seen multivibrators as frequency dividers in the repair work I've done. The clever thing here would be in the initialization, and synchronization at the receive end. I'd imagine that wheel has to be spun up to some fraction of 4000 rotations/second and uses photodiodes or perhaps just contact, to generate the starting pulses.

[1] https://www.turing.org.uk/sources/delilah.html

I'm frequently amazed how technological advance frequently is making things smaller/faster/cheaper, not inventing or discovering them in the first place.

True innovation is very expensive and very risky. It's unpalatable to most companies, so the best we've got is incremental improvements.

This is what government-funded universities should be doing, unprofitable research that automatically becomes public domain.

It always annoys me to no end, whenever somebody mentions about selling somebody's papers, but "putting a ban on their export", as if there is any difference whatsoever where is located some personal collection where they will rot. If it's considered a "national treasure", obviously, it cannot be sold to anyone, and quite honestly it MUST be scanned and be available on the internet for anybody interested to read it. If it's unimportant enough to be sold to a personal collection, it's also nobody's business what the buyer will do to that stuff.

This reminds me: are there even any good scans of the Portsmouth Papers that Keynes bought? Or is this stuff still just buried in various museum archives, seen only by certified friends of the museum's director?

> If it's considered a "national treasure", obviously, it cannot be sold to anyone ... If it's unimportant enough to be sold to a personal collection

It seems it already is owned by a private party, which is essentially the same as a personal collection.

Yeah, I think that was the GP's point: Then it either isn't "a national treasure", or it needs to be bought by the state.

Allocating a budget for that may be a major hurdle. Preventing national cultural heritage from being sold to someone outside the country seems to be a good compromise. If it is indeed "national cultural heritage".

I remember something like this was used in Cryptonomicon. It's been almost two decades since I read it, but IIRC it was a phone conversation between Churchill and FDR that was secured with twin one-time-pads encoded on vinyl records.

See: https://en.wikipedia.org/wiki/SIGSALY

I assumed also that this must of been done in some odd way in the analog domain, but apparently it was digital audio

Not really digital. The "combining unit" seems to have been an analog adder that wraps. The key generation was mechanical and digital, and produced an analog key waveform to add to the voice signal. At the other end,the analog waveform was subtracted out. Keeping both ends in sync would have been the main problem.

If it was a real A to D with digital encryption, it would have needed far more tubes. The digital side would have had to be all electronic. It wasn't. Look at the picture. That's an Enigma mechanism with a very few tubes out back.

Something like that would have sync problems. Not clear what they used as a time base for the demo device. Maybe for demo purposes they just used the power line as a clock.

Before SIGSALY, there was a pre-war Western Electric system, the A-3 [1], used for transatlantic phone calls. That had only five channels, advanced the key only every 15-20 seconds, and only had six channel-swapping patterns. The A-3 was a very low grade encryption system, and was broken by the Germans.

SIGSALY was the A-3 concept scaled up. More channels, faster key changes, additional analog processing. It filtered analog voice into ten channels, and swapped the channels around based on a one-time key stored on phonograph records. This seems to have taken way too much hardware. But it had redundancy, each direction was separate, and there was a pseudorandom key generator for testing without using up one-time keying material, all of which added bulk.

Audio speed analog to digital converters were invented in 1937 by Alec Reeves.[2] But they were not used until after WWII. A usable voice-speed A to D seems to have been beyond the capabilities of WWII electronics. Reeves had the basic concept - a counter, a ramp generator, and a comparator. All of those were very hard to do in 1937.

Reeves is an obscure figure. He invented pulse-code modulation as well as the A to D converter. He spent WWII working on aircraft navigation systems rather than encryption. If he'd been involved in encryption, high-security WWII voice encryption probably would have been all-digital. After the war, he was involved in the beginnings of fiber optic links, so he did quite a bit.

[1] http://chris-intel-corner.blogspot.com/2012/02/intercepted-c...

[2] https://en.wikipedia.org/wiki/Alec_Reeves

The UK's National Museum of Computing in Bletchley Park did a rebuild.[1] But not much detail is given in the video. Anybody know of a schematic? Turing's paper was quoted in Cryptologia, but that is paywalled now.

The 7-tube "combiner" is clearly analog. The key generator seems to be three multivibrators phase-locked with relatively prime ratios. That's cute. It's a pseudo-congruential random number generator in the analog domain.

This exploits the effect that oscillators that are weakly linked will tend to come into sync. Not necessarily at 1:1; you can sync at various ratios, with difficulty. Must have been a pain to get to work reliably. I'd like to see the schematics.

With phase-locked loops and counters this would be easy; that's how modern radio tuners work. Not easy to make reliable with 1940s technology. Getting things to sync up was a huge headache until the 1970s.

[1] https://www.hmgcc.gov.uk/news/turing-s-rebuilt-delilah-machi...

Delilah was the far superior system Turing never quite got to productionize, while the low-fi "Project X" was actually used for conversations between world leaders.

https://en.wikipedia.org/wiki/SIGSALY

> Work on the Delilah project stopped not long after the war ended, when Turing was hired by the British National Physical Laboratory to design and develop an electronic computer. Delilah “had little potential for further development,” Bayley said and “was soon forgotten.” Yet it offered a very high level of security, and was the first successful demonstration of a compact portable device for voice encryption.

That seems curious -- surely the military would have been interested in a finished portable voice encryption system, even after the war?

Turing did continue working for GCHQ after the war, which may have simply had Delilah delayed in favour of the main computer project. (We can see others working on similar things, like Claude Shannon, so the idea wasn't entirely abandoned).

However, in 1952 Turing was convicted of being gay and that meant he lost his security clearance. His name became anathema, and a lot of his projects were immediately buried or forgotten.

Great read but have a slightly off-topic question:

What is your opinion on visiting Bletchley Park? Is it worth it? Or is it more oriented to kids and whatnot?

In this context it's important to know that there are two museums at Bletchley and they aren't entirely co-operative with each other. There's The National Museum of Computing https://www.tnmoc.org/ and there's also Bletchley Park's museum https://bletchleypark.org.uk/ these are both on the same physical site, in the grounds of the Bletchley Park stately home because that's where Ultra happened in WW2

Both museums do have some kid-friendly activities, but their focuses are very different. You might wish to visit one, or both, and you should figure that out before going as they aren't even necessarily open at the same time.

TNMOC is about Computers generally, but has some exhibits about Enigma including a Bombe reconstruction and then of course Colossus - to break the Lorenz cipher, only exists due to the war and would have been at Bletchley. If you don't much care about Computers that's not too interesting, maybe worth a half hour if you've time.

The main Bletchley Park museum is about Codebreaking and particularly Ultra, the secret project to break German codes, most famously Enigma but also Lorenz and others, at Bletchley Park in WW2. It has some exhibits about spycraft, and a lot more about the practical undertaking of this codebreaking. Who are these people, what are they all doing here, what was their life like? If you care about the people you will want to visit this museum, but it has relatively little about the technical nuances of what was done.

It's probably gone now, but rather bizarrely there was a harrier jump jet parked on a patch of green grass when I was last there some years ago. Sort of "dumped, pending working out how to deal with it" which made me feel like nobody runs the place and everyone runs the place. "Joe said I could" -"oh OK put it over there then"

Another thing about the place is that modern archeology doesn't favour restoration of everything. Limited amounts of structural change happen. So a lot of the site looks like dismal ww2 badly poured concrete, not well looked after. Since GCHQ occupied the space for some time, some of it is probably post war, and historically relevant to different stories.

There was a whole bunch of random historical stuff, like a cinema museum with a collection of old projectors and a model railway at one point. It was really fun. Those had all gone last time I was there.

Also when I was last there, The National Museum Of Computing had free parking, but Bletchley Park museum charged for their car park, even though it is right next door. You could park at the computing museum car park and visit either or both.

One small past thread:

Alan Turing – The Delilah Project - https://news.ycombinator.com/item?id=38862147 - Jan 2024 (7 comments)

I take some solace that even 80 years ago the greatest mind in computer science was saying "damn, key synchronization is hard"

Did I miss the explanation of how the key synchronization worked? That seems mind boggling impossible

Slightly weirdly worded:

> Bell Labs’ pioneering SIGSALY speech-encryption system was constructed in New York City, under a U.S. Army contract, during 1942 and 1943. It was gigantic, weighing over 50 thousand kilograms and filling a room. Turing was familiar with SIGSALY and wanted to miniaturize speech encryption.

Well, yes; given that he _helped design it_ (https://en.wikipedia.org/wiki/SIGSALY#Development) he probably would be familiar with it.

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